POS1435 A GM-CSF AND IFN-Υ-DRIVEN PRO-INFLAMMATORY MACROPHAGE SIGNATURE IN POLYMYALGIA RHEUMATICA
Authors: W. F. Jiemy, A. Zhang, M. Sandovici, P. Heeringa, A. Diepstra, E. Brouwer, K. Van der Geest
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Polymyalgia rheumatica (PMR) is a common, rheumatic inflammatory disease. Synovial inflammation of the shoulder bursae and tendon sheaths is a hallmark feature of PMR. Data on the immune pathology of PMR are scarce, with glucocorticoid treatment remaining the mainstay treatment for this condition. An earlier study reported that macrophages dominate the inflammatory infiltrates in the synovium of PMR patients <sup>[1]</sup>. Recently, macrophages were identified as potent producers of IL-6 and GM-CSF in PMR bursa tissue <sup>[2,3]</sup>, while a strong IFN-γ signature was observed among bursa T cells <sup>[4]</sup>. GM-CSF and IFN-γ might potentially skew macrophages towards a pro-inflammatory phenotype. To what extent bursa macrophages in PMR also produce other pro-inflammatory cytokines remains unknown. <h3>Objectives:</h3> 1) To investigate the pro-inflammatory cytokine signature of bursa tissue macrophages in PMR. 2) To determine whether GM-CSF and IFN-γ stimulated monocytes adopt a pro-inflammatory macrophage phenotype. <h3>Methods</h3> Ultrasound-guided bursa tissue biopsies were obtained from 12 PMR patients with active disease. Immunohistochemistry staining for proinflammatory cytokines (IL-6, IFN-γ, IL-1β, TNF-α, IL-12, IL-23 and GM-CSF) and homeostatic cytokines M-CSF was scored quantitatively. Double immunofluorescence staining was performed linking cytokine expression to CD68+ macrophages. <i>In vitro</i> studies were performed with monocytes isolated from peripheral blood mononuclear cells of 8 patients with active PMR and 8 healthy donors. Monocytes were differentiated into macrophages during a 7-day culture in the presence of GM-CSF, with or without 24 hours co-incubation with IFN-γ on day 7 for additional polarization. Real-time qPCR was performed to determine expression of IL-6 in the cultured cells. <h3>Results</h3> CD68+ macrophages were the predominant immune cells in PMR bursa biopsies. IHC staining showed high expression (&gt;60% of positive cells) of proinflammatory cytokines (IL-6, IL-12, IL-23, TNF-α and GM-CSF) and the homeostatic cytokine M-CSF throughout the bursal tissue, while IFN-γ and IL-1β were moderately expressed (&gt;35% of positive cells). Double immunofluorescence staining confirmed the expression of these cytokines by the bursa tissue macrophages. <i>In vitro</i> experiments showed a slight upregulation of IL-6 expression when monocytes were differentiated into macrophages by GM-CSF. In the presence of IFN-γ, a substantially stronger upregulation of IL-6 was observed. In essence, similar <i>in vitro</i> findings were observed for monocytes/macrophages obtained from PMR patients and healthy controls. <h3>Conclusion</h3> Macrophages are the predominant immune cells in PMR bursa tissue and produce a wide array of pro-inflammatory cytokines. GM-CSF and IFN-γ may contribute to the pro-inflammatory phenotype of macrophages in PMR, as indicated by their strong ability to promote IL-6 expression <i>in vitro</i>. This study provides the first glance on the complex cytokine network present in key tissues affected by PMR. <h3>References</h3> [1]Meliconi, R et al. "Leukocyte infiltration in synovial tissue from the shoulder of patients with polymyalgia rheumatica. Quantitative analysis and influence of corticosteroid treatment." Arthritis and rheumatism vol. 39,7 (1996): 1199-207. [2]Jiemy, WF et al. "OP0015PROINFLAMMATORY MONOCYTES AND MACROPHAGES IN SYNOVIAL FLUID AND BURSAL TISSUE OF PATIENTS WITH POLYMYALGIA RHEUMATICA: POTENT PRODUCERS OF IL-6 AND GM-CSF." Annals of the Rheumatic Diseases 2022; 81:8-9. [3]Jiemy, WF et al. "Expression of interleukin-6 in synovial tissue of patients with polymyalgia rheumatica." Annals of the rheumatic diseases. 12 Aug. 2022 [4]Reitsema, RD et al. "Contribution of pathogenic T helper 1 and 17 cells to bursitis and tenosynovitis in polymyalgia rheumatica." Frontiers in immunology. 11 Aug. 2022 <h3>Acknowledgements</h3> This work was supported by a research grant from FOREUM Foundation for Research in Rheumatology and CSC scholarship for PhD students. The PMR Research On disease Mechanisms In Synovium (PROMIS) study was also funded by the Rheumatology Grant (Dutch Society for Rheumatology) and Mandema Stipend (University Medical Center Groningen). <h3>Disclosure of Interests</h3> William Febry Jiemy: None declared, Anqi Zhang: None declared, Maria Sandovici: None declared, Peter Heeringa: None declared, Arjan Diepstra: None declared, Elisabeth Brouwer Speakers bureau: E. Brouwer reports speaker and consulting fees from Roche in 2017-2018, outside the submitted work, Consultant of: E. Brouwer reports speaker and consulting fees from Roche in 2017-2018, outside the submitted work, Kornelis van der Geest Consultant of: K. van der Geest reports personal fees from Roche and AbbVie, outside the submitted work.